I have to rectify. The controller file is one thing (attenuation distance) but to play the effect at certain moments in time, then you do need an xml in which month, day, hour etc. are defined.
For instance:
<Effect
effectName=".................." (either the effect or the controller for the effect)
effectParams="HOD=16,16;MOH=00,60;"/>
where the effect will be played every day (because the days are not specified) at 16:00 hours during 60 minutes.
Of course you have to compile the xml into a bgl and put the bgl in the scenery folder of your scenery, the effect in the effects folder and the sound in the sound folder..